Which are the only two countries that have participated in all of the modern summer Olympic Games?

I'm going for Greece and Great Britain.

Cheers PJ (on the beat)

Greece is correct, but Great Britain is not.
They were absent from the 1904 games in St.Louis. There is one other correct answer.

Greece and Australia!
(mum and dad were born in the former, and this bloke in the latter!)

You got it, gtho4! These two countries have
always been able to put aside political concerns and send a team to the games. I was really upset when our President Carter decided to boycott the Moscow games in 1980.
It really did nothing but deny many athletes the chance to compete. I hope the political leaders of this century can resist the temptation to do anything like this again.
I'm looking forward to the games in Sydney this summer. Should be a great time!